Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C14/00—Alloys based on titanium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/002—Castings of light metals
  • B22D21/005—Castings of light metals with high melting point, e.g. Be 1280 degrees C, Ti 1725 degrees C

Definitions

• the invention relates to alloys based on titanium aluminides prepared using melt and powder metallurgy techniques and having an alloy composition of Ti - Al - y Nb with 44.5 atom% ⁇ z ⁇ 47 atom%, in particular
• Titanium aluminide alloys have properties suitable for a
• alloys which are based on an intermetallic phase ⁇ - (TiAl) with a tetragonal structure and, in addition to the majority phase ⁇ - (TiAl), also minority fractions of the intermetallic phase ⁇ 2 (Ti 3 Al) with hexagonal are of particular interest Structure included.
• This ⁇ - Titanium aluminide alloys are characterized by properties such as low density (3.85 to 4.2 g / cm 3), high elastic modulus, high strength and creep resistance up to 700 0 C, which they fabric as Werk ⁇ for moving components at elevated Make application temperatures attractive. Examples include turbine blades in aircraft engines and in stationary gas turbines, valves in engines and hot gas fans.
• Element boron a grain refinement can be achieved both in the cast state and after forming with subsequent heat treatment in the ⁇ -area.
• An increased proportion of ⁇ -phase in the microstructure due to low aluminum contents and high concentrations of ⁇ -stabilizing elements can lead to coarse dispersion of this phase and cause a deterioration of the mechanical properties.
• ⁇ - Titanaluminid alloys are due to their deformation and fracture behavior, but also because of the microstructural anisotropy of the preferred set lamellar Structure or duplex structure strongly anisotropic.
• different powder metallurgy and forming methods and combinations of these production methods are used.
• compositions may have outstanding combinations of properties.
• EP 1 015 605 B1 discloses a titanium aluminide alloy which has a structurally and chemically homogeneous structure. Here are the majority phases ⁇ (TiAI) and ⁇ 2 (Ti ß AI) finely dispersed.
• the disclosed titanium aluminide alloy with an aluminum content of 45 atom% is characterized by exceptionally good mechanical properties and high temperature properties.
• plastic fractions of> 1% are often sufficient for the applications mentioned in the introduction, manufacturers of turbines and engines require that this minimum level of ductility in industrial production be met by large amounts The lottery is guaranteed
• Ductility is sensitively dependent on the microstructure, it is extremely difficult in the industrial manufacturing process to ensure the most homogeneous microstructure possible.
• the maximum tolerable defect size e.g. the maximum grain or lamellar colony size, particularly small, so that a very high structural homogeneity is desirable for such alloys.
• the inevitable variations in the alloy composition of e.g. ⁇ 0.5 atom% in the AI content are difficult to achieve.
• duplex microstructures are considered for high temperature applications.
• the latter are formed on cooling from the single-phase region of the ⁇ -mixed crystal, in that plates of the ⁇ -phase precipitate crystallographically oriented from the ⁇ -mixed crystal.
• duplex microstructures consist of lamellar colonies and ⁇ grains and are formed when the material is annealed in the two-phase region ⁇ + ⁇ .
• the ⁇ grains which are present there are converted back into two-phase lamellar colonies on cooling.
• Coarse microstructure constituents are formed in ⁇ -titanium aluminide alloys mainly by forming large ⁇ grains as they pass through the ⁇ region. This can already happen during solidification, when large columnar crystals of the ⁇ -phase emerge from the
• the present invention seeks to provide a titanium aluminide alloy with a fine and homogeneous Gefömgemorphologie, occurring in industrial practice variations of the
• Alloy composition and unavoidable Temperatur ⁇ fluctuations in the manufacturing process hardly or not nen ⁇ to significantly affect the homogeneity of the alloy, in particular without fundamental changes in the manufacturing process. Furthermore, the object is to provide a component with a homogeneous alloy.
• This object is achieved by means of an alloy based on titanium aluminides prepared using melt and powder metallurgical techniques with an alloy composition of Ti - Al - y Nb with 44.5 atom% ⁇ z ⁇ 47 atom%, in ⁇ particular with 44.5 atom% ⁇ z ⁇ 45.5 atom%, and 5 atom% ⁇ y ⁇ 10 atom%, which is further developed by the fact that this molybdenum (Mo) in the range between 0.1 atom% to 3, 0 atom%, contains.
• the rest of the alloy is Ti (titanium).
• an alloy which can be used as a lightweight material for high temperature applications, e.g. Turbinen ⁇ blade or engine and turbine components, is suitable.
• the alloy according to the invention is produced using casting metallurgical, melt metallurgical or powder metallurgical processes or using these processes in combination with forming techniques.
• an alloy according to the invention has a composition of Ti-z Al-y Nb-x B with 44.5 atom% ⁇ z ⁇ 47 atom%, in particular with 44.5 atom% ⁇ z ⁇ 45.5 atom%,
• high-strength ⁇ -titanium aluminide alloys having a fine dispersion of the ⁇ -phase are used for a wide range
• the desired microstructure stability and process reliability is achieved by avoiding the occurrence of single-phase regions over the entire temperature range passed through in the production processes and during use by the targeted incorporation of the cubic-body-centered ⁇ -phase.
• the beta-phase occurs in all technical Titana- luminid alloys as the high-temperature phase at temperatures> 1350 0 C.
• Elements must be tuned very precisely to the Al content.
• undesired interactions occur which lead to high proportions of the ⁇ phase and to a coarse dispersion of this phase.
• Such a constitution is extremely disadvantageous for the mechanical properties.
• the properties of the ⁇ -phase also depend on the respective alloying elements and their composition.
• the constitution must be chosen so that an excretion of the brittle ⁇ -phase from the ⁇ -phase is largely avoided. Because of these relationships, a alloying composition is provided with which a composition and dispersion of the ⁇ -phase which is optimum for the mechanical properties can be realized for a wide range of process temperatures. At the same time, the best possible strength properties are achieved.
• the alloy also contains boron, preferably with a boron content in the alloy in the range of 0.05 atom% to 0.8 atom%.
• boron advantageously leads to the formation of stable precipitates which contribute to the mechanical hardening of the alloy according to the invention and stabilization of the microstructure of the alloy.
• the alloy contains carbon, preferably with a carbon content in the
• Fig. 2a to 2c each have a recording of a structure in one
• FIGS. 3a and 3b each show a picture of a microstructure in an alloy Ti - 45 Al - 5 Nb - 2 Mo (atom%) according to the invention by various method steps and FIGS. 3a and 3b
• FIG. 1 shows two photographs of a microstructure in a cast block of the alloy Ti - 45 Al - 8 Nb - 0.2 C (atom%).
• the recordings as well as all further recordings in the following figures were recorded by means of backscattered electrons in a scanning electron microscope.
• the microstructure (FIG. 1) shows lamellar colonies of the ⁇ 2 and ⁇ phases, which originated from former ⁇ -lamellae.
• the former ⁇ -lamellae are separated by strips of light-imaging grains of the ⁇ or B2 phase.
• the ⁇ -lamellae initially formed in the ⁇ - ⁇ -conversion decompose on further cooling in ⁇ 2 - and ⁇ -lamellae.
• FIGS. 2 a to 2 c show further photographs of the structure of the alloy T - 45 Al - 8 Nb - 0.2 C after various process steps in the scanning electron micrographs.
• Fig. 2a shows the structure after extrusion at 1230 0 C. Die
• Extrusion direction is horizontal.
• the microstructure shows grains of the oc 2 and ⁇ phases, with the cubic body-centered ⁇ phase disappearing.
• Fig. 2b shows the structure of the alloy after extrusion at 1230 0 C and another forging step at 1 100 0 C.
• the structure shows grains of the ci2 and ⁇ phase and a few ⁇ 2 / ⁇ lamellar colonies.
• Fig. 2c the structure of the alloy after extrusion at 1230 ° C and a subsequent heat treatment at 1330 0 C is shown.
• the microstructure also shows grains of the a ⁇ and ⁇ phases.
• the picture shows a fully lamellar microstructure with lamellae of ⁇ 2 and ⁇ phase.
• the lamellar colony size is approximately 200 ⁇ m, which also includes colonies that are significantly larger than 200 ⁇ m.
• FIG. 2a the cubic body-centered phase no longer occurs even in the structures shown in FIGS. 2b and 2c.
• the ⁇ -phase in this temperature range is thermodynamically unstable with a heat treatment after extrusion.
• FIGS. 3a and 3b Structures of an alloy according to the invention in two scanning electron micrographs are shown in FIGS. 3a and 3b. Starting from an alloy Ti - 45 Al - 5 Nb, the alloy molybdenum was alloyed with 2 atom%. This emerged
• Alloy Ti - 45 Al - 5 Nb - 2 Mo is based on a composition as described in European Patent EP 1 015 650 B1.
• Figures 3a and 3b illustrate the microstructure of this alloy erfindungsgemä ⁇ SEN observed after extrusion at 125O 0 C and a subsequent heat treatment at 1030 ° C (Fig. 3a) and at 1270 0 C (Fig. 3b).
• the microstructure in FIG. 3a shows grains of the ⁇ 2 , ⁇ and the light-forming ⁇ phases, the latter being arranged in strips.
• the microstructure in FIG. 3b shows lamellar colonies of the ⁇ 2 and ⁇ phases as well as grains of the light-forming ⁇ phase, from which in turn the ⁇ phase has been eliminated.
• FIGS. 3a and 3b are fine, very homogeneous and show a uniform distribution of the ⁇ -phase.
• After is a globular microstructure before, wherein grains of the beta-phase have arranged in strips parallel to the extrusion direction (Fig. 3a), while the at 127O 0 C punched material Jacques ⁇ a very homogeneous, fully -lamellar structure with uniformly distributed ß-grains has ( Figure 3b).
• the colony size of the microstructures of the alloy Ti - 45 Al - 5 Nb - 2 Mo is between 20 and 30 ⁇ m and is thus smaller by at least a factor of 5 than otherwise in fully lamellar microstructures of ⁇ - Titanium aluminide alloys.
• the ⁇ -phase is precipitated within the ⁇ -phase, so that the ⁇ -grains are subdivided very finely. As a result, a very fine and homoge ⁇ founded microstructure is achieved overall.
• the homogeneity of the alloys according to the invention in the range of relevant process temperatures does not depend on technically unavoidable fluctuations in the temperature or the composition.
• the titanium aluminide alloys of the present invention were prepared using casting or powder metallurgy techniques. For example, by hot forging, hot pressing or hot extrusion and hot rolling the erfindungsge ⁇ MAESSEN alloys can be processed.
• the invention offers the advantage that, in spite of the fluctuations in the alloy composition and process conditions occurring in industrial production, more reliable than before
• Titanium aluminide alloy is provided with a very uniform microstructure and high strength.
• the titanium aluminide alloy according to the invention achieves high strength up to a temperature in the range from 700 ° C. to 800 ° C. and good room temperature ductility.
• the legacy ments suitable for numerous applications and can be used, for example, for components subjected to particularly high loads or for exceptionally high temperatures for titanium aluminide alloys.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Physical Vapour Deposition (AREA)

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• 2004
  • 2004-11-23 DE DE102004056582A patent/DE102004056582B4/de not_active Expired - Fee Related
• 2005
  • 2005-09-01 CN CN2005800390124A patent/CN101056998B/zh not_active Expired - Fee Related
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• 2012
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